TPS54341_15 datasheet(15/48 Pages) TI

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REF

(ms)

(µA)

(nF) =

(V)

0.8

TPS54341

VIN

RUVLO1

UVLO2

ihys

VIN

UVLO1

UVLO2

Node

5.8 V

10 kW

TPS54341

www.ti.com

SLVSC61 – NOVEMBER 2013

DETAILED DESCRIPTION (continued)

Figure 26. Adjustable UVLO

Figure 27. Internal EN Pin Clamp

Soft-Start/Tracking Pin (SS/TR)

The TPS54341 device effectively uses the lower voltage of the internal voltage reference or the SS/TR pin

voltage as the reference voltage of the power-supply and regulates the output accordingly. A capacitor on the

SS/TR pin to ground implements a soft-start time. The TPS54341 device has an internal pullup-current source of

1.7

μA that charges the external soft-start capacitor. The calculations for the soft-start time (10% to 90%) are

shown in Equation 5. The voltage reference (VREF) is 0.8 V and the soft-start current (ISS) is 1.7 μA. The soft-start

capacitor should remain lower than 0.47

μF and greater than 0.47 nF.

(5)

At power up, the TPS54341 device does not start switching until the soft-start pin discharges to less than 54 mV

to ensure a proper power-up, see Figure 28.

Also, during normal operation, the TPS54341 device stops switching and the SS/TR must discharge to 54 mV,

when the VIN UVLO is exceeded, the EN pin pulls below 1.2 V, otherwise a thermal shutdown event occurs.

The FB voltage follows the SS/TR pin voltage with a 42-mV offset up to 85% of the internal voltage reference.

When the SS/TR voltage is greater than 85% on the internal reference voltage the offset increases as the

effective system reference transitions from the SS/TR voltage to the internal voltage reference (see Figure 23).

The SS/TR voltage ramps linearly until clamped at 2.7 V typically as shown in Figure 28.

Figure 28. Operation of SS/TR Pin When Starting

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